Metal layer forming methods and capacitor electrode forming methods

ABSTRACT

A capacitor electrode forming method includes chemisorbing a layer of at least one metal precursor at least one monolayer thick on a substrate, the layer including non-metal components from the precursor. The chemisorbed layer can be treated with an oxidant and the non-metal components removed to form a treated layer of metal. A capacitor electrode can be formed including the treated layer and, optionally, additional treated layers. Preferably, treating the layer does not substantially oxidize the metal and the treated layers exhibit the property of inhibiting oxygen diffusion. The chemisorbing and the treating can be performed at a temperature below about 450° C. or preferably below about 350° C.

TECHNICAL FIELD

The invention pertains to metal layer forming methods and capacitorelectrode forming methods.

BACKGROUND OF THE INVENTION

Capacitors are common devices used in electronics, such as integratedcircuits, and particularly semiconductor-based technologies. One commoncapacitor structure includes metal-insulator-metal (MIM) capacitors. Ahigh K factor (also known as dielectric constant or “κ”) dielectricmaterial may be desirable to enhance capacitance. Ta₂O₅ is one exampleof a high K factor dielectric, but it inherently oxidizes othercapacitor components when oxygen from the dielectric diffuses. Thediffused oxygen can form undesired interfacial dielectrics that reducean effective dielectric constant for the capacitor construction. Thediffused oxygen can also oxidize a capacitor electrode and reduce itsconductivity. Diffused oxygen might otherwise degrade performance ofcapacitor components. Use of other oxygen containing high K dielectricmaterials has proved to create similar problems.

SUMMARY OF THE INVENTION

According to one aspect of the invention, a capacitor electrode formingmethod includes chemisorbing a layer of at least one metal precursor atleast one monolayer thick on a substrate, the layer including non-metalcomponents from the precursor. The method includes treating thechemisorbed layer with an oxidant and removing the non-metal componentsto form a treated layer consisting essentially of metal. Thechemisorbing, treating, and removing can be repeated sufficient to format least one additional treated layer consisting essentially of metal onthe treated layer. A capacitor electrode can be formed consisting of thetreated layers. By way of example, the metal layers can exhibit theproperty of inhibiting oxygen diffusion to a greater extent than wouldanother layer of same composition and thickness formed without thechemisorbing. Also, both the chemisorbing and the treating can beperformed at a temperature below about 450° C. Further, treating thelayer can be performed in a manner avoiding substantially oxidizing themetal.

In another aspect of the invention, a capacitor electrode forming methodincludes chemisorbing a layer of at least one metal precursor andtreating the chemisorbed layer with an oxidant to form a treated layerconsisting essentially of a metal. The metal can include iridium,osmium, or mixtures thereof. The chemisorbing and treating can berepeated to form a capacitor electrode comprising the treated layers.

According a further aspect of the invention, a metal layer formingmethod includes atomic layer depositing a layer on a substrate usingprecursor material including at least one of methylcyclopentadienylplatinum trimethyl ((CH₃C₅H₄)Pt(CH₃)₃) and cyclooctadienyl platinumdimethyl ((C₈H₁₁)Pt(CH₃)₂), the layer including platinum and organiccomponents from the precursor material. The method includes treating thelayer with an oxidant and removing the organic components to form atreated layer consisting essentially of platinum. As an example, thetreated layer can consist essentially of one saturated monolayer.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention are described below withreference to the following accompanying drawings.

FIG. 1 shows a fragmentary, sectional view of a capacitor constructionformed by a method according to one aspect of the invention.

FIG. 2 shows a scanning electron microscope micrograph of platinumformed within an opening by a method according to one aspect of theinvention.

FIG. 3 shows an atomic concentration depth profile of a platinum layerformed on a titanium nitride layer by a method according to one aspectof the invention.

FIG. 4 shows an atomic concentration depth profile of the platinum layerin FIG. 3 after rapid thermal oxidation annealing.

FIG. 5 shows an atomic concentration depth profile of a platinum layerformed on a titanium nitride layer by a method according to anotheraspect of the invention.

FIG. 6 shows an atomic concentration depth profile of the platinum layerin FIG. 5 after rapid thermal oxidation annealing.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Atomic layer deposition (ALD) involves formation of successive atomiclayers on a substrate. Such layers may comprise an epitaxial,polycrystalline, amorphous, etc. material. ALD may also be referred toas atomic layer epitaxy, atomic layer processing, etc. Further, theinvention may encompass other deposition methods not traditionallyreferred to as ALD, for example, chemical vapor deposition (CVD), butnevertheless including the method steps described herein. The depositionmethods herein may be described in the context of formation on asemiconductor wafer. However, the invention encompasses deposition on avariety of substrates besides semiconductor substrates.

In the context of this document, the term “semiconductor substrate” or“semiconductive substrate” is defined to mean any constructioncomprising semiconductive material, including, but not limited to, bulksemiconductive materials such as a semiconductive wafer (either alone orin assemblies comprising other materials thereon), and semiconductivematerial layers (either alone or in assemblies comprising othermaterials). The term “substrate” refers to any supporting structure,including, but not limited to, the semiconductive substrates describedabove.

Also in the context of the present document, “metal” or “metal element”refers to the elements of Groups IA, IIA, and IB to VIIIB of thePeriodic Table of the Elements along with the portions of Groups IIIA toVIA designated as metals in the periodic table, namely, Al, Ga, In, TI,Ge, Sn, Pb, Sb, Bi, and Po. The Lanthanides and Actinides are includedas part of Group IIIB. “Non-metals” refers to the remaining elements ofthe periodic table.

Described in summary, ALD includes exposing an initial substrate to afirst chemical specie to accomplish chemisorption of the specie onto thesubstrate. Theoretically, the chemisorption forms a monolayer that isuniformly one atom or molecule thick on the entire exposed initialsubstrate. In other words, a saturated monolayer. Practically, asfurther described below, chemisorption might not occur on all portionsof the substrate. Nevertheless, such an imperfect monolayer is still amonolayer in the context of this document. In many applications, merelya substantially saturated monolayer may be suitable. A substantiallysaturated monolayer is one that will still yield a deposited layerexhibiting the quality and/or properties desired for such layer.

The first specie is purged from over the substrate and a second chemicalspecie is provided to chemisorb onto the first monolayer of the firstspecie. The second specie is then purged and the steps are repeated withexposure of the second specie monolayer to the first specie. In somecases, the two monolayers may be of the same specie. Also, the secondspecie might not add a monolayer, but rather chemisorb onto and removesome portion of the first monolayer. Further, a third specie or more maybe successively chemisorbed and purged just as described for the firstand second species.

Purging may involve a variety of techniques including, but not limitedto, contacting the substrate and/or monolayer with a carrier gas and/orlowering pressure to below the deposition pressure to reduce theconcentration of a specie contacting the substrate and/or chemisorbedspecie. Examples of carrier gases include N₂, Ar, He, etc. Purging mayinstead include contacting the substrate and/or monolayer with anysubstance that allows chemisorption byproducts to desorb and reduces theconcentration of a contacting specie preparatory to introducing anotherspecie. The contacting specie may be reduced to some suitableconcentration or partial pressure known to those skilled in the artbased on the specifications for the product of a particular depositionprocess.

ALD is often described as a self-limiting process, in that a finitenumber of sites exist on a substrate to which the first specie may formchemical bonds. The second specie might only bond to the first specieand thus may also be self-limiting. Once all of the finite number ofsites on a substrate are bonded with a first specie, the first speciewill often not bond to other of the first specie already bonded with thesubstrate. However, process conditions can be varied in ALD to promotesuch bonding and render ALD not self-limiting. Accordingly, ALD may alsoencompass a specie forming other than one monolayer at a time bystacking of a specie, forming a layer more than one atom or moleculethick. The various aspects of the present invention described herein areapplicable to any circumstance where ALD may be desired. A few examplesof materials that may be deposited by ALD include platinum, iridium,ruthenium, osmium, palladium, or mixtures thereof, titanium nitride, andothers.

Often, traditional ALD occurs within an often-used range of temperatureand pressure and according to established purging criteria to achievethe desired formation of an overall ALD layer one monolayer at a time.Even so, ALD conditions can vary greatly depending on the particularprecursors, layer composition, deposition equipment, and other factorsaccording to criteria known by those skilled in the art. Maintaining thetraditional conditions of temperature, pressure, and purging minimizesunwanted reactions that may impact monolayer formation and quality ofthe resulting overall ALD layer. Accordingly, operating outside thetraditional temperature and pressure ranges may risk formation ofdefective monolayers.

The general technology of chemical vapor deposition (CVD) includes avariety of more specific processes, including, but not limited to,plasma enhanced CVD and others. CVD is commonly used to formnon-selectively a complete, deposited material on a substrate. Onecharacteristic of CVD is the simultaneous presence of multiple speciesin the deposition chamber that react to form the deposited material.Such condition is contrasted with the purging criteria for traditionalALD wherein a substrate is contacted with a single deposition speciethat chemisorbs to a substrate or previously deposited specie. An ALDprocess regime may provide a simultaneously contacted plurality ofspecies of a type or under conditions such that ALD chemisorption,rather than CVD reaction occurs. Instead of reacting together, thespecies may chemisorb to a substrate or previously deposited specie,providing a surface onto which subsequent species may next chemisorb toform a complete layer of desired material. Under most CVD conditions,deposition occurs largely independent of the composition or surfaceproperties of an underlying substrate. By contrast, chemisorption ratein ALD might be influenced by the composition, crystalline structure,and other properties of a substrate or chemisorbed specie. Other processconditions, for example, pressure and temperature, may also influencechemisorption rate.

According to one aspect of the invention, a metal layer forming methodincludes chemisorbing a layer of at least one metal precursor at leastone monolayer thick on a substrate. The at least one metal precursor caninclude a variety of metal elements, such as platinum, iridium,ruthenium, osmium, palladium, or mixtures thereof, as well as othermetal elements. Since more than one metal precursor can be used, avariety of options exist for the precursors. For example, precursorscould be selected containing different metals such that a resultingmetal layer is a mixture, such as an alloy, of the different metals.Also, precursors could be selected containing the same metal, butcontaining different non-metal components of the precursor. A fewexamples of possible precursors include, but are not limited to,MeCpPt(Me)₃ (methylcyclopentadienyl platinum trimethyl((CH₃C₅H₄)Pt(CH₃)₃)), CpPt(Me)₃ (cyclopentadienyl platinum trimethyl((C₅H₄)Pt(CH₃)₃)), (COD)Pt(Me)₂ (cyclooctadienyl platinum dimethyl((C₈H₁₁)Pt(CH₃)₂)), cis-[PtMe₂(MeNC)₂], Pt(acetylacetonate)₂,Pt(hexafluoroacetylacetonate), Pt(PF₃)₄, Pt(CO)₂Cl₂, etc.

In using a precursor, the chemisorbed layer can include non-metalcomponents from the precursor. In the case of organometallic precursors,the non-metal component included in the chemisorbed layer can be anorganic component. Similarly, in the case of inorganic metallicprecursors, the non-metal components can be inorganic components. It isconceivable that the chemisorbed layer might include both organic andinorganic non-metal components from the precursor.

Accordingly, the method further includes treating the chemisorbed layerto form a treated layer consisting essentially of metal. One possiblemethod of treating the chemisorbed layer includes contacting the layerwith an oxidant and removing the non-metal components. Even so, treatingthe layer preferably does not substantially oxidize the metal. Dependingon the metal and the non-metal component of a precursor, some portion ofthe chemisorbed metal layer might be oxidized during treatment. Forexample, platinum is considered resistant to oxidation. Thus, atreatment method can be selected that uses oxidants.

In particular, a wide variety of oxidants can be used in treatment ofchemisorbed platinum precursor to form a treated layer consistingessentially of platinum with little concern -for oxidizing the platinum.Preferred oxidants include O₃, O₂, N₂O, H₂O₂, SO₃, H₂O, etc.Understandably, a small amount of oxidation might occur and/or a smallamount of non-metal component might remain yet the treated layer canstill be considered not substantially oxidized and/or consistessentially of metal.

Criteria for determining a sufficient purity for the treated layer canbe determined by those of ordinary skill taking into account theintended use and properties of a bulk metal layer that will include thetreated layer. A statistically insignificant amount of oxidation ornon-metal component might remain such that the treated layer consistingessentially of metal exhibits a statistically same conductivity comparedto a treated layer consisting purely of metal. The type and amount oftreatment and/or oxidant might warrant careful selection for other metalelements more susceptible to oxidation in comparison to platinum.

Essentially, treatment of the chemisorbed layer can be focused onbreaking chemical bonds between non-metal components and the chemisorbedmetal and, possibly, chemical bonds between non-metal components and thesubstrate. Example process conditions are described herein for aparticular precursor and substrate. However, those of ordinary skill candetermine appropriate process conditions for other precursors andsubstrates using chemical and physical property data currently availablefor such materials.

Purging is one additional process condition of note. As described above,ALD often uses purging (including evacuation) criteria thatsubstantially prevent mixing of a precursor and an oxidant. Accordingly,a metal forming method can further include purging excess precursor fromover the substrate prior to treating the chemisorbed layer with anoxidant. Also, the method can include purging the oxidant from over thesubstrate prior to chemisorbing any additional layers.

A further process condition of note is the chemisorption temperature andthe treating temperature. Such temperatures can be different, butpreferably they are both below 450° C. More preferably, both thechemisorbing and the treating are performed at a temperature below about350° C. Still lower temperatures are also conceivable, such as about100° C. Notably, oxidant strength can be one factor in providing a lowtreating temperature. For example, O₃ is a stronger oxidant than O₂ andcan allow a lower treating temperature.

One advantage of the described low temperatures includes preventingspontaneous degradation of precursors. Precursors can be sensitive totemperature during chemisorbing and/or treating such that they degradeprior to chemisorption, possibly preventing true chemisorption, andinstead only physically deposit on the substrate. Such physicaldeposition can result in forming defective monolayers such that filmstep coverage and/or desired properties are impacted. Degradation ofchemisorbed precursors during or before treatment might yieldby-products that are not removed as effectively by the treatment incomparison to chemisorbed precursors that have not degraded. Holding tothe temperature guidelines described herein can assist in preventingprecursor degradation and insuring efficient chemisorption andtreatment.

A metal layer forming method may be used to form a treated layerconsisting essentially of one saturated monolayer. The metal layer mayalso be more than one monolayer thick. Accordingly, the method caninclude sufficiently repeating the chemisorbing, the treating, and theremoving to form at least one additional treated layer consistingessentially of metal on the treated layer. Successive treated layers canbe provided to a desired thickness depending on a particularapplication.

The metal layer described herein can be suitable for use as a capacitorelectrode. The small physical dimensions of some capacitors createdemanding specifications for step coverage in forming the capacitorelectrodes. The various aspects of a metal layer forming methoddescribed herein can be used to provide superior step coverage in acapacitor. In addition, observation indicates that the metal layersformed by the described methods can exhibit the property of inhibitingoxygen diffusion to a greater extent than would another layer of samecomposition and thickness formed without the chemisorbing or withoutatomic layer depositing.

As an inhibitor of oxygen diffusion, a metal layer can be incorporatedinto a capacitor in a variety of ways, including as an entire electrodeor as part of an electrode with other parts formed by different methods.According to one aspect of the invention, a capacitor electrode formingmethod can be used to form treated layers consisting essentially ofmetal and forming a capacitor electrode consisting of the treatedlayers. In this manner, the entire capacitor electrode helps inhibitoxygen diffusion. Such a capacitor electrode may be particularlysuitable as a bottom electrode of a capacitor that often has a smallerthickness as compared to a top electrode.

FIG. 1 shows a capacitor construction 10 that includes a substrate 12having a capacitor opening 14 formed therein. A bottom electrode 16 isformed within capacitor opening 14 and on substrate 12. A dielectriclayer 18 is formed on bottom electrode 16 and a top electrode 20 isformed on dielectric layer 18. Notably, the structures shown in FIG. 1can be supplemented with additional capacitor structures according tothe knowledge of those skilled in the art. Also, the structures shown assingle layers can be multiple layer structures.

Substrate 12 can include at least one of insulative and semiconductivematerial. Capacitor opening 14 can be formed within insulative materialand a conductive connection provided to a semiconductive diffusionregion (not shown). Also, capacitor opening 14 can be formed throughinsulative material and into an underlying semiconductive materialhaving a diffusion region. Further, substrate 12 can be a semiconductivematerial of which all or a portion comprises a diffusion region.

Thus, chemisorbing a layer of at least one metal precursor at least onemonolayer thick can occur on insulative material, such as within acapacitor opening to form a bottom electrode. As an alternative, aconductive layer can be formed as part of a capacitor electrode andadditional metal formed thereon by a method according to the variousaspects of the invention. Titanium nitride is one example of aconductive layer. In such manner, the substrate on which chemisorbingoccurs can be a conductive layer that is included in a capacitorelectrode. In a still further alternative, treated layers consistingessentially of metal can be first formed and additional metal formedthereon by a method other than ALD. The combination of methods might beuseful in forming a top electrode which often has a greater thicknesscompared to a bottom electrode.

With reference to FIG. 1, a method according to one aspect of theinvention can include chemisorbing a layer of at least one metalprecursor at least one monolayer thick on dielectric layer 18, treatingthe chemisorbed layer to form a treated layer consisting essentially ofmetal, and forming additional metal on the treated layer by some othermethod. It is conceivable that the treated layer so formed can exhibitthe property of inhibiting oxygen diffusion. In light of the aboveoptions for forming an electrode, oxygen diffusion from dielectric layer18 and other sources can be reduced with a capacitor electrode formedaccording to one of the various aspects of the invention.

Turning to the Figures, FIG. 2 shows the conformal nature of a platinumlayer atomic layer deposited on BPSG and FIG. 3-6 provide an oxygendiffusion comparison. FIG. 3 shows an atomic concentration depth profileobtained by X-ray Photoelectron Spectroscopy (XPS) of an approximately250 Angstrom thick platinum layer formed on a titanium nitride layer.Notably, the bulk of the platinum layer is free of carbon and oxygen towithin detection limits and some carbon and oxygen is shown on theplatinum layer surface at 0 Angstroms. Also, the oxygen content withinthe TiN layer around the platinum interface is about 15 atomic percent.FIG. 4 shows an atomic concentration depth profile obtained by XPS forthe platinum layer of FIG. 3 after a 650° C. rapid thermal oxidationanneal. The bulk of the platinum layer is carbon and oxygen free towithin detection limits and the surface oxygen is comparably reduced.Oxygen content in the TiN layer around the platinum interface increasedto about 22 atomic percent, but the platinum layer and the titaniumnitride layer are otherwise unaffected by the oxidation anneal.Accordingly, FIG. 4 demonstrates the oxygen diffusion inhibitionproperties of the platinum layer.

Forming the platinum layer of FIGS. 3 and 4 was performed whilemaintaining a titanium nitride surface temperature of 100° C. andbeginning with a 5 second exposure to MeCpPt(Me)₃ vapor followed by a 5second, 50 SCCM helium purge. Oxidation was performed with a 50 SCCMflow of ozone for 5 seconds and then followed by a 5 second, 50 SCCMhelium purge. The cycles were repeated to form the 250 Angstrom platinumlayer.

FIG. 5 shows an atomic concentration depth profile obtained by XPS of anapproximately 370 Angstrom platinum layer on a titanium nitride layer.Some surface carbon and oxygen and interfacial oxygen are noted. FIG. 6shows an atomic concentration depth profile of the FIG. 5 platinum layerafter a 650° C. rapid thermal oxidation anneal. Notably, oxygen contentin the platinum layer increased slightly and the former titanium nitridelayer is shown completely oxidized. The platinum layer thus deposited isshown to be ineffective at inhibiting oxygen diffusion.

Forming the platinum layer of FIGS. 5 and 6 was performed whilemaintaining a titanium nitride surface temperature of 190° C. andbeginning with a 5 second exposure to MeCpPt(Me)₃ vapor followed by a 5second, 50 SCCM helium purge. Oxidation was performed with a 50 SCCMflow of oxygen for 5 seconds and then followed by a 5 second, 50 SCCMhelium purge. The cycles were repeated to form the 370 Angstrom platinumlayer. Although the platinum layer was of suitable quality, the propertyof inhibiting oxygen diffusion was reduced either by the temperatureincrease, the change in oxidant, or some combination of the two.

In compliance with the statute, the invention has been described inlanguage more or less specific as to structural and methodical features.It is to be understood, however, that the invention is not limited tothe specific features shown and described, since the means hereindisclosed comprise preferred forms of putting the invention into effect.The invention is, therefore, claimed in any of its forms ormodifications within the proper scope of the appended claimsappropriately interpreted in accordance with the doctrine ofequivalents.

1-33. (canceled)
 34. A capacitor electrode forming method comprising:chemisorbing a layer of at least one metal precursor at least onemonolayer thick on a substrate, the layer comprising non-metalcomponents from the precursor; treating the chemisorbed layer at atemperature of between 100 and 190° C. with an oxidant effective toremove the non-metal components to form a treated layer consistingessentially of metal; sufficiently repeating the chemisorbing, thetreating, and the removing to form at least one additional treated layerconsisting essentially of metal on the treated layer; and forming acapacitor electrode consisting of the treated layers.
 35. The method ofclaim 34 wherein the non-metal components comprise organic components.36. The method of claim 34 wherein the oxidant comprises O₃.
 37. Themethod of claim 34 wherein treating the layer does not substantiallyoxidize the metal.
 38. The method of claim 34 wherein both thechemisorbing and the treating are performed at a temperature between 100and 190° C.
 39. The method of claim 34 wherein the treated layersexhibit the property of inhibiting oxygen diffusion to a greater extentthan would another layer of same composition and thickness formedwithout the chemisorbing.
 40. The method of claim 34 wherein thecapacitor electrode consists of a bottom electrode and the substratecomprises insulative material.
 41. The method of claim 34 wherein thetreating occurs after purging excess metal precursor that is notchemisorbed and without mixing the metal precursor and the oxidant.